Finally!! Us Mac users are used to waiting a little longer than PC users to get a compatible version of the game, but 15 years must be some kind of record.
It almost made it out way back when, but was cancelled at the last minute. There’s an interview with one of the developers about it on Youtube: http://www.youtube.com/watch?v=JBg6L4H7WdE
https://developer.valvesoftware.com/wiki/Valve_Time